The present invention relates to a method for transmitting V5 protocols in a cascaded V5 interface, as defined in the preamble or claim 1.
V5 interface standards ETS 300 324 and ETS 300 347 describe an interface between a local exchange and an access network and the functionality in each network element. The access network is the part of a local area network that contains the subscriber""s lines. Thus, subscribers and subscriber""s lines can be connected to the exchange either directly (direct subscribers) or via various multiplexers and/or concentrators. V5 interfaces enable subscribers belonging to a physically separate access network to be connected to a local exchange using a standard interface.
A dynamic V5.2 concentrator interface as defined in the ETS 300 347 standard series consists of one or more (1-16) PCM (Pulse Code Modulation) lines. One PCM line comprises a total of 32 channels, each with a transfer rate of 64 kbit/s, i.e. 2048 kbit/s altogether. The V5.2 interface supports analogue telephones as used in the public telephone network, digital, such as ISDN (Integrated Services Digital Network) basic and system subscriber lines as well as other analogue or digital terminal equipment based on semi-fixed connections.
A static V5.1 multiplexer interface consistent with the ETS 300 324 standard series consists of one 2048 kbit/s PCM line. The V5.1 interface supports the same subscriber types as the V5.2 interface except ISDN system lines.
Terminal equipment can be connected to the subscriber ports of an access node. One access node may have one or more V5 interfaces connected to it. Subscriber ports are created in the V5.1 interface by associating an unambiguous address of each subscriber port with a given address in the V5.1 interface. In the local exchange, this address is created as a V5 subscriber. In other words, each subscriber port has an unambiguous address which is coupled with a V5.1 interface address and which uses a certain time slot (analogue subscribers) or certain time slots (ISDN subscribers) for communication with the local exchange. In the V5.2 interface, too, each subscriber port has an unambiguous address, but the signalling to the local exchange is implemented using a dynamically allocated time slot/dynamically allocated time slots. This means that the BCC (Bearer Channel Control) protocol as defined in the V5 standard allocates the time slots to be used separately for each call.
V5 standardisation aims at creating an open interface for use between a local exchange and an access network. However, no interface for use between the access node and the subscribers within the access network has been defined. Therefore, problems are encountered in connecting subscribers to the access node e.g. via a static concentrator interface (V5.1). A further problem is that, especially in an environment with multiple suppliers, the solutions of different suppliers for concentrating subscribers in an access network differ significantly from each other, which means that operators do not necessarily have enough choice options regarding suppliers of equipment.
A special problem associated with the cascading of V5 interfaces is that the network element transmitting messages does not necessarily have to implement all the states of the V5 interface port control status engine because, according to the standard, these states are in any case implemented in the local exchange and in the access node or concentrator closest to the subscriber. If the message transmitting network element were provided with status engines implementing all the states of the port control status engine, this would be likely to cause status conflicts between the local exchange, the message transmitting network element and the access node or concentrator closest to the subscriber.
The object of the present invention is to eliminate the drawbacks described above
A specific object of the present invention is to disclose a new type of status engine for a message transmitting network element. The solution of the invention is designed to simplify the status engine so as to render it easier to encode and test than a standard status engine.
The telecommunication system of the invention for implementing ISDN user port status monitoring comprises a telephone exchange with a number of subscribers defined in it in the normal manner. The telecommunication system also comprises a first access node, which is connected to the telephone exchange via a first V5 interface, a second access node, which is connected to the first access node via a second V5 interface, and a subscriber terminal connected to the second access node. The connection between the subscriber and the telephone exchange, the access network, is formed by cascading the two V5 interfaces. In the method of the invention, the states of the user ports are monitored in different network elements using status engines appropriate for this purpose.
According to the invention, all ISDN user port activation messages are transmitted through the status engine of the first access node, which in this embodiment works as a message transmitting network element, without changing its status when the current status of the status engine is other than the BLOCKED state consistent with the specification.
As compared with prior art, the present invention has the advantage that, in the message transmitting network element, preferably the first access node mentioned above, it is possible to use the same status engine for PSTN and ISDN user ports. Moreover, the message transmitting network element need not take care of the various stages of the call after the user port has been set to the OPERATIONAL state. Therefore, the activation and deactivation messages transmitted in ISDN signalling need not be heeded.
In addition, the solution of the invention allows easier testing of the subscriber ports and the operation of a cascaded V5 interface. At the same time, the error potential is reduced, thus making the system more reliable.
In an embodiment of the invention, the ISDN user port status engine of the first access node is implemented using states consistent with the PSTN user port status engine. To implement this, the status engines monitoring the states of the ISDN user ports of the first access node are preferably identical with the status engines of PSTN user ports. Depending on the application, it is possible to implement in the first access node separate status engines for both PSTN and ISDN user ports or a common status engine for both port types because the status engines are substantially identical in respect of functionality.
The second access node is preferably a multiplexer or a concentrator. In addition, In an embodiment of the method, the first V5 interface is a V5.2 interface consistent with the ETS 300 347 standard series and the second V5 interface is a V5.1 interface consistent with the ETS 300 324 standard series.